1. Field of the Invention
The present invention relates to display devices. In particular, the present invention relates to liquid crystal display devices, and further, to a technique for reducing power consumption.
2. Description of the Related Art
EL display devices, plasma displays, liquid crystal display devices, and the like are given as examples of display devices. For example, a liquid crystal display device which is one example of them is driven by inverting a polarity of a voltage to be applied to a pixel electrode with respect to a potential of an opposite electrode (common potential) every certain period, in order to prevent deterioration of a liquid crystal material, reduce display unevenness (mura) such as flickers, keep display quality, and so on. Such driving method is called as inversion driving.
As examples of the inversion driving, frame inversion driving, source line inversion driving, gate line inversion driving, dot inversion driving, common inversion driving, and the like can be given (for example, see Reference 1: Japanese Published Patent Application No. H 11-231822).
Frame inversion driving is a driving method in which a polarity of a voltage to be applied to a pixel electrode is inversed with respect to a common potential every frame period. FIG. 8 shows a display pattern diagram of the frame inversion driving. Note that the display pattern diagram shown in FIG. 8 shows a model screen having display pixels of 3 rows×4 columns as an example for simplification. Since the frame inversion driving has a long inversion period of polarities, flickers are easy to be recognized visibly. In order to reduce flickers, the frame inversion driving and source line inversion driving, gate line inversion driving, dot inversion driving, or the like are combined in general.
The gate line inversion driving is a driving method in which a polarity of a voltage to be applied to each pixel is inverted every gate line. FIG. 9 shows a display pattern diagram of the gate line inversion driving. Note that the display pattern diagram shown in FIG. 9 shows a model screen having display pixels of 3 rows×4 columns as an example for simplification.
The source line inversion driving is a driving method in which a polarity of a voltage to be applied to each pixel is inverted every source line. FIG. 10 shows a display pattern diagram of the source line inversion driving. Note that the display pattern diagram shown in FIG. 10 shows a model screen having display pixels of 3 rows×4 columns as an example for simplification.
The dot inversion driving is a driving method in which a polarity of a voltage to be applied to a pixel electrode is inverted every pixel, and which is made by combining the source line inversion driving and the gate line inversion driving. FIG. 11 shows a display pattern diagram of the dot inversion driving. Note that the display pattern diagram shown in FIG. 11 shows a model screen having display pixels of 3 rows×4 columns as an example for simplification.
In addition, when the frame inversion driving, the source line inversion driving, the gate line inversion driving, the dot inversion driving or the like is adopted, an amplitude width of a potential of a video signal written into a source signal line is needed to be twice as large as that of when inversion driving is not conducted (when driving with only one polarity of a voltage to be applied to a pixel electrode with respect to a common potential.). Thus, as compared with the case where the inversion driving is not conducted (when driving with only one polarity of a voltage to be applied to a pixel electrode with respect to a common potential, i.e., driving without inverting the polarity of a voltage), power consumption becomes high as well as high resistance to voltage of a driver circuit is necessary. Then, in the case of the frame inversion driving or the gate line inversion driving, common inversion driving is further adopted in some cases.
The common inversion driving is a driving method in which a polarity of a common potential is inverted in synchronization with timing of polarity inversion of a potential of a pixel electrode, and an amplitude width of a potential of a video signal written into a source signal line can be reduced by half by the common inversion driving.
There is also a case where inversion driving is conducted for an EL display device for the sake of lengthening a lifetime of an EL element, not only for a liquid crystal display device (for example, see Reference 2: Japanese Published Patent Application No. 2001-222255).